Polymers and copolymers prepared or modified by using cobalt complexes

ABSTRACT

A polymerization process comprising the steps of admixing a halogen-containing compound, monomer, and a cobalt complex.

This application claims the benefits of provisional application No.60/121,895 filed Feb. 26, 1999.

TECHNICAL FIELD

The present invention is generally directed toward a polymerizationprocess and the polymeric products resulting therefrom. Moreparticularly, the polymerization process of this invention employs acobalt complex and a halogen-containing compound to carry out thepolymerization process. Advantageously, the process of the presentinvention provides block and graft copolymers, allows for thefunctionalization of halogenated polymers, and also provides a processwhereby halogenated polymers can be crosslinked.

BACKGROUND OF THE INVENTION

Cobalt complexes, such as cobaloximes, have been used as chain transferagents in free radical polymerizations. It is believed that the chaintransfer process proceeds with the abstraction of a hydrogen atom frompolymeric radicals and transfer to a new monomer to initiate a newpolymer chain. As a result, cobalt complexes have been used to controlthe molecular weight of polymers synthesized from methacrylate estersand styrene.

This catalytic chain transfer, however, has only been observed in thecase of methacrylic monomers and styrene. The polymerization of acrylateesters, vinyl esters monomers, and acrylonitrile monomers in thepresence of cobalt complexes results in inhibition. Studies have shownthat the cobalt forms a relatively stable bond with the polymer chain.By introducing electromagnetic energy, however, researchers have foundthat the cobalt-carbon bond that is formed between a polymer chain andthe cobalt complex is photolabile. Therefore, the introduction ofelectromagnetic energy to these polymerization systems has led to thediscovery that the polymerization of acrylates will proceed according topseudo-living polymerization mechanisms. Moreover, certainorgano-cobaloxime compounds have been photo-initiated in the presence ofmonomer to form block and graft copolymers.

SUMMARY OF THE INVENTION

Extensive research of the mechanisms involved in both the catalyticchain transfer and pseudo-living polymerization reactions that employcobalt complexes has led to the discovery that cobalt complexes, such ascobaloximes, will abstract a halogen atom from a halogenated polymer andthereby form a free radical on a polymer. This research has also led tothe unexpected discovery that the polymerization of acrylate esters willproceed in the presence of thermal energy in lieu of electromagneticenergy where cobalt complexes in the presence of halogen-containingcompounds are used as initiators. Advantageously, these discoveries haveled to the formation of grafted polymers from halogenated precursors.These discoveries have also led to the formation of block copolymersthat employ thermal energy in lieu of electromagnetic energy in thepolymerization process. Still further, these discoveries have providednew methods by which halogenated and unsaturated polymers can becrosslinked.

In general, the present invention provides a polymerization processcomprising the steps of admixing a halogen-containing compound, monomer,and a cobalt complex.

The present invention also includes a process for forming amethacrylate-functionalized polymer comprising the steps of admixing ahalogen-containing polymer, a cobalt complex, and a methacrylate ester,and heating the admixture.

The present invention further provides a process for formingpolyacrylate-functionalized polymer comprising the steps of admixing ahalogen-containing polymer, a cobalt complex, and acrylate monomer, andheating the admixture.

The invention also includes a process for forming a copolymer comprisingthe step of admixing a polymer with at least two halogen substituents, acobalt complex, and monomer.

The present invention further includes a process for crosslinking anunsaturated polymer.

The present invention also provides a process for crosslinking ahalogenated polymer comprising the step of admixing a halogenatedpolymer and a cobalt complex.

PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION

The present invention generally provides a process whereby a cobaltcomplex and a halogen-containing compound can be used to initiate thepolymerization of monomers. As a result, block or graft copolymers canbe formed, halogenated polymers can be functionalized, and halogenatedor unsaturated polymers can be crosslinked.

The term cobalt complex refers to cobaloximes and organocobaloximes aswell as cobalt porphyrins and mixtures thereof. These cobalt complexesmay be referred to as cobalt (II) and cobalt (III) chelates, and aredescribed in U.S. Pat. Nos. 5,847,060, 5,770,665, 5,756,605, 5,726,263,5,028,677, 4,886,861, 4,694,054, and 4,680,352, which are incorporatedherein for this purpose. Additionally, these compounds can be referredto as macrocyclic cobalt complexes as described in U.S. Pat. No.5,468,785. Cobaloximes and organocobaloximes are preferred because theycan be easily prepared.

Cobaloximes include a central cobalt atom that is surrounded by twodimethylglyoxime moieties in its equatorial plane. The cobalt atomcontains an unpaired electron that causes the compound to beparamagnetic and to have chemical properties similar to a stable freeradical. The central cobalt atom is in the +2 oxidation state. A Lewisbase is coordinated to the cobalt atom below the plane in which the twodimethylglyoxime moieties reside.

The coordinating Lewis base ligand below the equatorial plane caninclude any Lewis base that does not destroy the essentially planarconfiguration of the equatorial ligands. Non-limiting examples of theseLewis bases include pyridine and triphenylphosphine.

Organocobaloximes are similar compounds except that they include anadditional organic group above the equatorial plane. The central cobaltatom, therefore, is in the +3 oxidation state, and they are diamagneticmaterials that do not have the chemical characteristics of freeradicals. Organocobaloximes may also be referred to asorganobis(dimethylglyoximato)cobalt complexes. The organic group thatmay be coordinated above the equatorial plane (in the case of anorganocobaloxime) can include any non-tertiary organic group thatlikewise does not destroy the essentially planar configuration of theequatorial ligands. Accordingly, besides this proviso, the selection ofany specific organic group for coordination above the equatorial planeshould not limit the scope and practice of the present invention.Non-limiting examples of these organic groups can include alkyl groupsthat include from 1 to about 30 carbon atoms, α-carbethoxyethyl,isopropyl, 2-hydroxy-1-butyl, ω-chloroalkyl, and ω-hydroxyalkyl.Preferred organic groups are those that would be attached by secondarycarbon atoms to cobalt in the organocobaloxime. Typical examples includeisopropyl, α-carbethoxyethyl, and 2-butyl. Many of the cobaloximes andorganocobaloximes that are useful in practicing the present inventionhave been described in U.S. Pat. No. 5,468,785, which is fullyincorporated herein by reference. In addition to cobaloximes andorganocobaloximes, the cobalt complexes that can be used in practicingthe present invention also include those that have been defined in U.S.Pat. No. 4,886,861, which is fully incorporated herein by reference.

Cobalt porphyrins include cobalt complexes of hematoporphyrin IXterramethyl ether, the cobalt complex of ethylporphyrin-1, cobalttetraphenyl porphyrin, cobalt protoporphyrin dimethylether, and cobaltphthalocyanine. These compounds have been described as catalysts forchain transfer reactions in methacrylate ester polymerizations byEnikolopyan, et al., J. Polym. Sci., Vol. 19, pp. 878-889 (1981),Smirnov, Polym. Sci. U.S.S.R., Vol. 23, pp. 1169 (1981), and Cacioli J.Macromol. Sci., Vol. 1723, pp. 839-852 (1986). An example of a cobaltporphyrin that is a catalyst for pseudo-living polymerization ofacrylate esters is neopentyl(tetramesitylporphyrinato) cobalt asdiscussed by Wayland, J. Am. Chem. Soc., Vol. 116, pp. 7943-7944.

Organocobaloximes are preferred because cobaloximes are very reactivecompounds that readily react with oxygen and may therefore beinconvenient to directly use. Although organocobaloximes are much easierto store and handle, they must be converted to useful cobaloxime. Thiscan be achieved by heating or by irradiating the mixture with light.Thus, the preferred reactions of the present invention involve theformation of a cobaloxime “in situ” by thermally or photochemicallyinduced disassociation of an organocobaloxime.

The bond strengths of the carbon-cobalt bonds in compounds such asorganocobaloximes are approximately 20 kcal/mole, which is generallyvery low. They therefore are easily induced to dissociate by exposure totemperatures as low as 70° C. or by photolysis to form the cobaloximeneeded for the radical-forming reactions. This dissociation isillustrated below:

where R¹ represents an organic group, and [Co] represents a cobaltcomplex such that R¹[Co] is an organo-cobalt complex. As mentionedabove, cobaloximes have the chemical characteristics of free-radicals,and [Co] therefore represents a radical.

Cobalt complexes are generally soluble but could be immobilized to aninsoluble substrate such as crosslinked polystyrene, alumina, or silica.This would have the advantage, particularly for the catalytic chaintransfer reactions, of immobilizing the cobalt complex so that it couldbe easily separated from the reaction mixture. Attachment of the cobaltcomplex to an insoluble substrate could occur if the axial base were asubstituted pyridine or phosphine that was chemically bonded to thesubstrate. Alternatively, it could occur if the equatorial ligand werebonded to the substrate. This invention therefore includes both solubleand immobilized organocobalt complexes.

The halogen-containing compounds can be any compound or polymercontaining one or more reactive carbon-halogen bonds. Those withcarbon-chlorine or carbon-bromine bonds are preferred, and compounds orpolymers with carbon-bromine bonds are most preferred. Compounds orpolymers with several chlorine or bromine atoms attached to the samecarbon atom are more reactive than those with fewer carbon-halogenbonds. Accordingly, those compounds or polymers containing more than onehalogen atom are preferred.

If the carbon atom that is attached to the halogen atom is likewiseattached to a group that can stabilize the free radical that eventuallyforms, then the free radical generation process is facilitated. Typicalradical stabilization groups include, for example and withoutlimitation, phenyl groups, carbonyl groups including those present inesters, ketones, aldehydes and anhydrides, nitrile groups, vinyl groups,and substituted vinyl groups.

Non-limiting examples of reactive halogen compounds include CCl₄, CBr₄,CBrCl₃, CCl₃COOR (where R is an alkyl group, substituted alkyl group,aryl, substituted aryl, etc. group), ΦCH₂Br, ΦCH₂Cl, CCl₃CH₃, ΦCHCl₂ andCCl₃COCCl₃. In general, compounds with aromatic carbon-halogen bondswill not be effective in the present processes unless they also containaliphatic carbon-halogen bonds.

Halogenated polymers are also useful. These polymers will include atleast one carbon-halogen bond at their chain ends, attached pendant totheir backbone, or attached to organic groups that may be pendant fromtheir backbone. These halogen atoms can be arranged in any combinationand be included in any number. The polymers can be prepared bycopolymerization reactions in which at least one of the monomerscontains a reactive carbon-halogen bond, by polymerization orcopolymerization reactions that are initiated by initiators that containreactive carbon-halogen bonds, or by polymerization or copolymerizationreactions conducted in the presence of chain transfer agents thatcontain reactive carbon-halogen bonds. The polymers could also be madeby polycondensation processes. In fact, any polymerization method can beemployed to make the halogen-substituted polymers including, withoutlimitation, free radical, anionic, cationic, ring opening, metathesis,and polycondensation polymerization methods. The halogen-substitutedpolymers can also be prepared by chemically modifying existing polymersby halogenation, acylation, esterification, and other reactions.Non-limiting examples of these polymers include styrene-butadienecopolymers containing chloromethylstyrene units, brominatedisobutylene-isoprene copolymers, and unsaturated polyesters containingreactive halogen atoms. An example of a halogenated polymer thatcontains halogen atoms bound to a pendant group is a copolymer ofstyrene and chloromethylstyrene.

In general, the presence of a higher number of halogen atoms, either asgrafts or at the chain ends of the polymer, will increase the reactivityof the halogen substituted polymer with the cobalt complex. Thus, asthose skilled in the art will readily appreciate, the chemical andphysical properties of the end product will be more or lesssignificantly changed depending upon the amount of halogen present inthe polymer. Also the desired proportion of carbon-halogen bonds presentin the polymer will depend upon the chemical and physical propertiesdesired for a particular application.

Many monomers can be polymerized by using the process of the presentinvention. For example, these monomers may include acrylate esters,methacrylate esters, methacrylamides, vinyl esters, vinyl aromatics, andunsaturated nitrites. Where methacrylate esters, methacrylamides, andvinyl aromatics, such as styrene, are employed, it is believed that thepolymerization carried out by the process of the present invention willproceed by a free-radical polymerization reaction that includescatalytic chain transfer. On the other hand, where acrylate esters,vinyl esters, and acrylonitriles are employed, it is believed that thepolymerization of this invention will proceed by way of a pseudo-livingpolymerization. These mechanisms and their impact on the polymerizationconditions and results are discussed in greater detail hereinbelow.

The methacrylate ester monomers that are useful in practicing thepresent invention can generally be defined by the formula:

where R³ includes an organic group. The organic group can includealiphatic groups, cycloaliphatic groups, aromatic groups, and polymericgroups. Preferably R³ will include simple alkyl groups such as methyl,ethyl, propyl, etc. up to about 20 carbon atoms. Although these groupsare carbon based, they can include hetero atoms such as oxygen,nitrogen, sulphur, silicon, and phosphorus. Preferred methacrylate estermonomers include methyl methacrylate, ethyl methacrylate, propylmethacrylate, t-butyl methacrylate, phenyl methacrylate, hydroxyethylmethacrylate, and N,N-dimethylmethacrylamide.

The acrylate monomers that are useful in the pseudo-livingpolymerization process of the present invention include any ester thatcan generally be defined by the following formula:

wherein R³ includes an organic group as defined above. The preferredmonomers include methylacrylate, ethyl acrylate, propyl acrylate,t-butyl acrylate, phenyl acrylate, or hydroxyethyl acrylate, andN,N-dimethylacrylamide.

As an optional component of the polymerization admixture, a reducingagent may be employed. As will be discussed in greater detailhereinbelow, the combination of the cobalt complex and halogenatedcompound form a halocobalt compound. This compound can be converted backinto a useful cobalt complex by reacting it with a reducing agent. As aresult, the cobalt complex can function as a catalyst.

The reducing agents that are preferably employed in practicing thepresent invention include those that are able to reduce thehalogen-cobalt compounds back to cobalt (II) complexes such ascobaloxime. It is preferable that the reducing agents not be so reactivethat they would reduce functional groups such as esters, aldehydes, ornitrile groups that may be within the monomers or polymers within thereaction mixture. Examples of these reducing agents include zinc, iron,copper, and hydrogen. The most preferred reducing agent is elementalzinc.

It should be appreciated that halogen-cobalt compounds can be employedinstead of organocobalt compounds if zinc or other reducing agents arepresent because the reduction reaction will generate the cobalt (II)complex, e.g., cobaloxime, that is needed for radical generation andpseudo-living or catalytic chain transfer steps. This technique is veryadvantageous because compounds such as chlorocobaloxime are very stable,readily available, and inexpensive. In fact, it is envisioned to employchlorocobaloximes, as well as other similar chlorine-containingcompounds, to be used as curing systems for halogen-containingelastomers.

It is generally preferred to carry out the polymerization of thisinvention in a solvent, although some polymerization may be conducted inbulk monomer.

Typical solvents for the reaction include hexane, benzene, toluene,acetone, methyl ethyl ketone, tetrahydrofuran, methylcellusolve,dioxane, and decalin. Halogenated solvents are also useful. Mixtures ofthe foregoing solvents may also be employed.

The amount of cobaloxime that is useful in practicing this invention canvary depending upon the temperature and the reactivity of thecarbon-halogen bonds in the halogen-containing compound and the averagenumber of monomer units that are desired. Where halogenated polymers areemployed it has been found useful to admix from about 0.05 to about 20parts by weight catalyst per one hundred parts by weight halogenatedpolymer (phr). Preferably, the admixture should contain from about 1 toabout 10 parts by weight catalyst phr, and even more preferably itshould contain from about 2 to about 4 parts by weight catalyst phr. Inthe event that non-polymeric halogenated compounds are employed, theamount of cobalt complex that is useful will generally range form about0.05 to about 2.0 moles of cobalt per mole of halogenated compound.

Where halogenated polymers are employed, the amount of methacrylatemonomer that is admixed can vary depending upon the average number ofmethacrylate units that are desired to be present in the blocks orgrafts. In general, it has been found useful to admix from about 10 toabout 5,000 parts by weight methacrylate monomer phr. Preferably, theadmixture should contain from about 50 to about 1,000 parts by weightmethacrylate monomer phr, and even more preferably it should containfrom about 100 to about 500 parts by weight methacrylate monomer phr.

Where halogenated polymers are employed, it has been found useful toadmix from about 0.5 to about 100 parts by weight reducing agent phr.Preferably, the admixture should contain from about 5 to about 20 phr,and even more preferably it should contain from about 5 to about 10 phr.The amount of reducing agent that is used within the admixture can varydepending upon the amount of cobalt complex employed and the reactivityof the halocobalt compound byproduct derived from the reactionmechanism.

The process of this invention can be practiced by admixing a cobaltcomplex, a halogenated compound, and monomer by using standard mixingtechniques. There is no specific order in which the reactants need to beadmixed.

In the preferred embodiments of this invention, the reaction mixture isheated, although it should be appreciated that heat may not be requiredto initiate polymerization in those situations where extremely reactivehalogen-containing compounds are employed. Where extremely reactivehalogen-containing compounds are employed, however, the polymerizationreaction is not easily controlled. In those embodiments where lessreactive halogenated compounds are employed to polymerize methacrylateesters or similar monomers, the reaction mixture is preferably heated toa temperature from about 35° C. to about 150° C., more preferably fromabout 50° C. to about 120° C., and most preferably to about 70° C. Atthese elevated temperatures, catalytic chain transfer is more likely tooccur. In those embodiments that employ acrylate monomers in conjunctionwith less reactive halogenated compounds, a controllable pseudo-livingpolymerization will occur, although heat is typically required.Accordingly, these polymerization are typically conducted at atemperature from about 70° C. to about 150° C. Inasmuch as it hasunexpectedly been discovered that acrylate monomers, as well as similarmonomers, can be polymerized according to the present invention by usingheat in lieu of electromagnetic energy, the embodiments of thisinvention that are directed toward the polymerization of acrylate orsimilar monomers are preferably conducted in the absence of appreciableelectromagnetic energy.

Generally, the formation of the desired reaction product is evidenced byan increase in the viscosity of the polymerization mixture. The productsof polymerization, except for those intentionally crosslinked, willgenerally be isolated by filtrating the reaction mixture to removeunchanged reducing agents and byproducts (e.g., zinc chloride when zincis employed), removing a portion of the monomer and solvent by vacuumdistillation, and subsequently pouring the remaining solution into anon-solvent for the polymer. The precipitated polymer can then beisolated by filtration and drying. Those skilled in the art, however,can readily select other reaction and isolation techniques. Thispolymerization process can also occur within a reactive extruder.

It is believed that an organic radical is formed by the dissociation ofthe organo-cobalt complex. This radical is capable of initiatingpolymerization. Once an organocobaloxime dissociates, however, theorganic radical and cobaloxime rapidly recombine and regenerate theoriginal non-radical organo-cobalt complex. The recombination process isstrongly exothermic and therefore the concentration of organic radicalsin equilibrium with cobaloxime will be very low. Nonetheless, the rateof the dissociation reaction will be high because of the low energybonds between the organic radicals and the cobalt atom in cobaloximes.Thus, organocobaloximes dissociate rapidly and reversibly to formorganic radicals and cobaloxime, but the equilibrium strongly favors theorganocobaloximes.

The equilibrium between organocobaloximes and their dissociationproducts is disturbed by adding halogen-containing compounds toorgano-cobalt complex solutions. This causes the cobalt complex to beconverted into a stable halocobaloxime that is unable to participate inthe equilibrium, thereby driving the equilibrium reaction in thedirection of dissociation to produce useful organic radicals.

When this reaction is conducted in the presence of monomers, apolymerization ensues. By varying the structure of the organocobaloximeor the organic halide, and by varying the concentrations of thesematerials or the reaction temperature, it is possible to vary thepolymerization rate over a wide range.

It is believed that organic halogen compounds have an importantinfluence on free radical polymerizations mediated by cobaloxime andorganocobaloximes. The reactions of cobaloximes with organic halidesform halocobaloximes and free radicals that are necessary to sustain thepolymerization reaction despite the fact that conventional radicaltermination reactions slowly remove growing polymer chains from thesystem. Additionally, these reactions can advantageously be used tocreate growing polymer chains. For example, new growing polymer chainscan be formed when an organic halide such as CCl₄, CHCl₃, CHBr₃ andΦ-CH₂Cl is employed. Also, growing polymer chains can be formed when thereactant R²[HAL] is a polymer containing at least one halogen atom boundeither pendant to its backbone or at its chain end is employed. Blockcopolymers can be formed when the halogen atoms are located at the endof the polymer chains. On the other hand, if the halogen atoms arependant to the polymer, grafted copolymers can result.

Thus, the reactions of cobalt complexes with halogen-containingcompounds yield radicals that initiate polymerization reactions in aconventional way. The location of the radical on the organic halogencompound or polymer corresponds to the location of the substitutedhalogen atom. Thus, these polymerization reactions can lead to theformation of new polymers, block copolymers, or graft copolymersdepending upon the structure of the halogen substituted compounds orpolymers employed. Also, the reactions of cobalt complexes with polymersthat are substituted with halogen atoms pendant to the backbone of thepolymer yield polymer radicals that can either form crosslinks byreacting with other polymer radicals in the absence of monomers orinitiate polymerization reactions in the presence of monomers.

It is also believed that the initiation of polymerization reactions inthe presence of methacrylate monomers brings about catalytic chaintransfer reactions that produce polymers bearing methacrylate-typeunsaturation at their chain ends or pendant to their backbone. On theother hand, the initiation of polymerization reactions in the presenceof acrylate monomers brings about pseudo-living polymerization reactionswhereby block copolymers or graft polymers can be produced.

The catalytic chain transfer reactions can cause some of themethacrylate monomer to form oligomers, such as dimers or trimers, whichcontain unsaturated chain ends. These materials can also causemethacrylate esters to add to the growing methacrylate grafts by anaddition/fragmentation process, and the oligomer radicals that areproduced by this process can decompose to regenerate monomer or reactwith polymer radicals to form grafted or block segments that do not haveunsaturated ends. Although this process likely occurs, the side reactionthat leads to the formation of these oligomers does not necessarilydetract from the overall process. In fact, this process can subsequentlyinitiate the formation of unsaturated poly(methyl methacrylate)oligomers by a normal catalytic chain transfer process. Thus, the graftor block copolymer may be obtained as a mixture with these oligomers. Inmany applications, such as surface coating, it may be satisfactory touse the mixture as such. The oligomers, however, can also be removed byprecipitation. For example, when the process involves the catalyticchain transfer process, the poly(methyl methacrylate) oligomer fractioncan be recovered by an appropriate extraction process and reused toreplace some of the monomer in subsequent polymerization reactions. Infact, all of the monomer can be replaced by the oligomer fraction. Themethacrylate-functionalized polymer can then be separated and purifiedby employing conventional techniques including precipitation.

If a methacrylate ester is present, catalytic chain transfer reactionsoccur during the grafting process leading to the formation of shortpoly(methyl methacrylate) grafts having methyl methacrylate unsaturatedchain end functionalities. As will be discussed below, polymerscontaining these grafts are extremely valuable for surface coating andcasting applications.

While catalytic chain transfer reactions can be initiated by cobaltcomplexes in the presence of halogenated compounds or polymers andmethacrylate monomers, it is believed that pseudo-living polymerizationsoccur when the monomers are acrylate or other vinyl monomers. In thepseudo-living polymerizations involving acrylate monomers, the samecobalt complexes. halogen-containing compounds, and polymers areemployed.

This reaction mechanism is very conducive to the creation of graftedpolymers and block copolymers. Advantageously, a polymer may befunctionalized with a variable number of carbon-halogen bonds branchingfrom the backbone of the polymer such that the reaction of thehalogen-functionalized polymer with a cobalt complex in the presence ofacrylate monomer creates a polymer with multiple acrylate grafts. Thispseudo-living process for forming grafted polymers is different from thecatalytic chain transfer reactions involving methacrylate monomers andallows for the production of block copolymers.

To form multi-block copolymers or block copolymer grafts, thetermination of the growing acrylate chain through recombination with thecobalt complex radical is exploited. Upon termination, additional, butdifferent, monomer may be introduced to the system before thepolymer-cobalt bond is broken by thermolysis, such that, uponthermolysis, the new monomer will add to the acrylate chains until theirgrowth is, in turn, terminated through combination with the cobaltcomplex radical. Then, the acrylate monomer can be reintroduced into thesystem to grow an acrylate block, and so on.

As discussed above, the reaction of cobalt complexes, such ascobaloximes, with organic-halogen compounds leads to the formation ofstable halocobalt compound byproducts, such as halocobaloximes. Althoughinert, these compounds remove reactive cobalt complexes from thereaction mixture and therefore one cobalt complex molecule is requiredfor each free radical generated. This process can be made more efficientby providing the reaction mixture with a reducing agent, such as zincdust, that will convert the halocobalt byproduct back to a useful cobaltcomplex, as shown in the following reaction mechanism:

2HAL[Co]+Zn→2[Co]+Zn(HAL)

The use of the these reducing agents to increase the efficiency ofradical generation is one preferred embodiment of this invention.

As discussed above, the polymerization process of this invention cangive rise to a variety of useful polymeric structures that may varybased upon the reactants and polymerization conditions employed.

The methacrylate-functionalized polymers that are formed by the processof this invention are unique materials. They contain terminalmethacrylate double bonds that are connected by only carbon-carbon bondsto the polymer backbone. These methacrylate-functionalized polymers areextremely useful for forming coatings and castings because they caninclude numerous methacrylate functional groups along the backbone ofthe polymer. As a result, low molecular weight materials can be producedthat have a relatively low viscosity and that can be quickly cured toform high molecular weight films, coatings and castings. Thesefunctionalized polymers can advantageously include a multitude ofmethacrylate functionalities, which make these polymers especiallyuseful for coating and casting applications.

Other useful polymer structures is a polyacrylate-functionalizedpolymers. Because the polymerization mechanism leading to the formationof these grafted polymers is believed to proceed by way of apseudo-living polymerization, the resulting product can be synthesizedto include long or high molecular weight polyacrylate grafts that arenearly gel-free.

Still other polymeric structures that can result from the practice ofthe present invention include block copolymers. Advantageously, thesecopolymers can be used as thermoplastic elastomers, dispersants,compatibilizers, thickeners, and surface active materials.

The discoveries relating to the use of cobalt complexes in conjunctionwith halogen-containing compounds have also led to new processes wherebyhalogenated polymers or unsaturated polymers can be crosslinked. In thecase of halogenated polymers, the reaction between a halogenated polymerand a cobalt complex will generate a free radical on the polymer chainthat can combine with similar free radicals on other polymers chains toachieve a crosslink. Where polymerizable monomer is present, the freeradicals can initiate polymerization and thereby form crosslinks betweenpolymeric chains.

In the case where it is desirable to crosslink unsaturated polymers, thecombination of cobalt complexes and halogenated compounds will againform free radicals that will react with double bonds on the unsaturatedpolymeric chain. As a result, cobalt complexes in conjunction withhalogenated compounds can serve to crosslink unsaturated polymers.

In order to demonstrate the practice of the present invention, thefollowing examples have been prepared and tested as described in theGeneral Experimentation section disclosed herein below. The examplesshould not, however, be viewed as limiting the scope of the invention.The claims will serve to define the invention.

GENERAL EXPERIMENTATION

The cobalt complexes (cobaloximes and organocobaloximes) that wereemployed within the experiments taught within this written descriptionwere prepared by using the techniques employed by Schrauzer et al.(Chem. Ber., 1964, 97,3056 & J. Am. Chem. Soc., 1967, 98, 1999).

EXAMPLE 1

Poly(chloromethylstyrene-co-styrene) was functionalized with methylmethacrylate. Specifically, (pyridinato)cobaloxime (0.05 g), methylmethacrylate (10 g), and poly(chloromethylstyrene-co-styrene) (1.0 g),were mixed and heated at about 70° C. for about three hours. Thepoly(chloromethylstyrene-co-styrene) contained about 20.4 mol percentchloromethylstyrene.

The product was isolated and was then analyzed by HNMR. The HNMRspectrum contained multiple methoxy and α-methyl proton resonances atabout 3.5 and about 1 ppm indicating the presence of methyl methacrylateunits at the graft junction. In addition, resonances at about 5.5 andabout 6 ppm indicated the presence of unsaturated methyl methacrylateunits. The relative areas of the various resonances present in thisspectrum together with the molecular weight of this polymer indicatedthat the grafted copolymer had an average of 4.1 grafts per chain and anaverage number of methyl methacrylate units per graft of 6.5.

EXAMPLE 2

Poly(chloromethylstyrene-co-styrene) was functionalized with methylmethacrylate. Specifically, (pyridinato)cobaloxime (0.01755 g), zinc(0.47025 g), methyl ethyl ketone (1.0780 g), methyl methacrylate (0.9289g), and poly(chloromethylstyrene-co-styrene) (0.29575 g), were mixed andheated at about 70° C. for about 46 hours. Thepoly(chloromethylstyrene-co-styrene) contained about 20.4 mol percentchloromethylstyrene.

The polymer product was isolated by precipitating the product in 40 mlof methanol followed by extraction with methanol overnight. Evidencerevealed a product yield of about 0.1443 g.

EXAMPLE 3

Ethyl acrylate was polymerized by using mixtures of organocobaloximesand chloroform at 70° C. Specifically, mixtures containing ethylacrylate (10 mL), a specified amount of an organocobaloxime (See TableI) and chloroform (2 mL) were prepared and divided into 10 crim-sealvials. Each vial was sealed with a Teflon™ coated butyl rubber crim-sealseptum, and its contents were purged with argon. The vials were wrappedin foil and heated at 70° C. for various times. The vials were thencooled at room temperature, weighed on an analytical balance, and placedin a vacuum oven at 45° C. in 1 mm of Hg until they reached a constantweight.

The conversion was calculated by comparing the initial weight of asample with the weight of the dried sample. The weight of theorganocobaloxime was ignored because it never was more than 0.25 molpercent of the reaction mixture.

Samples for molecular weight determination were dissolved in THF and thesolutions were filtered. Molecular weights were determined by using gelpermeation chromatography with polystyrene standards. The results thatwere obtained are summarized in Table I. The following abbreviationswere used for the cobaloxime compounds: IpPyCo refers toisopropyl(pyridinato)cobaloxime, EaPyCo refers toα-carboethoxyethyl(pyridinato)-cobaloxime, and tBaPyCo refers to1-(tert-butoxycarbonyl)ethyl(pyridinato)-cobaloxime.

TABLE I Cobaloxime Polymerization Compound Cobaloxime (g) Ethyl acrylate(g) Chloroform (g) Time (Hr) Conversion (%) M_(n) IpPyCo 0.095 9.82 2.9411 35 20,800 IpPyCo 0.047 10.61 2.97 47.9 72 54,700 IpPyCo 0.024 9.662.99 25.6 57 76,800 EaPyCo 0.126 9.38 3.21 6.9 59 27,700 EaPyCo 0.0629.79 3.23 25.4 85 46,800 EaPyCo 0.015 4.77 0.99 48.5 77 115,632  tBaPyCo0.113 10.00 3.63 7.5 59 28,100 tBaPyCo 0.056 9.73 3.43 25.7 80 53,100

EXAMPLE 4

Following the general procedure set forth in the preceding example,t-butyl acrylate (4.47 g) was heated with1-(tert-butoxycarbonyl)ethyl(pyridinato)cobaloxime (0.02 g) andchloroform (2.13 g) at 70° C. The results set forth in Table II wereobtained by using the procedure set forth in the preceding example.

TABLE II Polymerization Time (Hr) Conversion (%) M_(n) M_(w)/M_(n) 0.927 17,600 1.8 2.0 62 23,500 1.7 4.4 79 20,500 2.0 6.2 91 19,600 1.7 19.0100 16,200 2.0

EXAMPLE 5

Following the general procedure set forth in the preceding example,benzyl acrylate (5.3 g) was heated withα-carboethoxyethyl(pyridinato)-cobaloxime (0.04 g) and chloroform (1.79g) at 70° C. The results set forth in Table III were obtained by usingthe procedure set forth in the preceding example.

TABLE III Polymerization Time (Hr) Conversion (%) M_(n) M_(w)/M_(n) 1.135 20,900 2.8 5.1 46 18,000 2.1 37.0 66 22,400 1.8 59.7 73 17,000 2.0

EXAMPLE 6

Following the general procedure set forth in the preceding example,ethyl acrylate (4.76 g) was heated withα-carboethoxyethyl(pyridinato)-cobaloxime (3.45 g) and bromoform (3.45g) at 70° C. The results set forth in Table IV were obtained by usingthe procedure set forth in the preceding example.

TABLE IV Polymerization Time (Min) Conversion (%) 7 36 15 58 30 66 61 78123 90

EXAMPLE 7

Following the general procedure set forth in the preceding example,ethyl acrylate (9.69 g) was heated withα-carboethoxyethyl(pyridinato)-cobaloxime (0.126 g) and1,1,1-trichloroethane (3.16 g) at 70° C. The results set forth in TableV were obtained by using the procedure set forth in the precedingexample.

TABLE V Polymerization Time (Hr) Conversion (%) M_(n) M_(w)/M_(n) 0.619.5 37,200 2.9 1.0 20.3 44,900 2.0 2.0 35.1 51,500 2.9 4.0 70.4 45,9001.9 7.0 80.2 48,900 1.9

EXAMPLE 8

Following the general procedure set forth in the preceding example,methyl methacrylate (5.02 g) was heated withα-carboethoxyethyl(pyridinato)-cobaloxime (0.03 g) and carbontetrachloride (1.68 g) at 70° C. The results set forth in Table VI wereobtained by using the procedure set forth in the preceding example.

TABLE VI Polymerization Time (Hr) Conversion (%) M_(n) M_(w)/M_(n) 5 8934,300 2.2 10 85 34,500 2.5 32 98 34,700 2.1

EXAMPLE 9

A mixture of methyl methacrylate (4.93 g),α-carboethoxyethyl(pyridinato)-cobaloxime (0.03 g) and methyltrichloroacetate (1.59 g) was heated for five minutes at 70° C.Poly(methyl methacrylate) was obtained (93% yield), and wascharacterized as having a M_(n) of 99,900 and a molecular weight(M_(w)/M_(n)) distribution ratio of 3.58. Polymerization occurredquickly, and therefore it was concluded that there was littleopportunity for catalytic chain transfer reactions to occur which gaverise to the high molecular weight products that were formed.

EXAMPLE 10

A mixture of styrene (4.79 g), α-carboethoxyethyl(pyridinato)-cobaloxime(0.03 g) and carbon tetrachloride (1.68 g) was heated at 70° C. for 21hours. Polystyrene having a molecular weight (M_(n)) of 3,040 and amolecular weight distribution (M_(w)/M_(n)) of 2.5 was obtained in 38percent yield.

EXAMPLE 11

Following the general procedure set forth in Example 9, styrene (4.79 g)was heated with α-carboethoxyethyl(pyridinato)-cobaloxime (0.03 g) andmethyl trichloroacetate (1.60 g) at 70° C. The results set forth inTable VII were obtained by using the procedure set forth in Example 9.

TABLE VII Polymerization Time (Hr) Conversion (%) M_(n) M_(w)/M_(n) 1434 970 12.8 58 38 — — 186 48 1,160 7.4 1250 66 2,060 2.8

These results show that catalytic chain transfer takes place in thispolymerization system.

EXAMPLE 12

A copolymer of styrene and chloromethylstyrene was prepared.Specifically, a mixture of styrene (8 ml), chloromethylstyrene (2 ml),azobisisobutylonitrile (0.082 g) and benzene (10 ml) was purged withargon and heated at 70° C. for four hours. The mixture was then pouredinto a large volume of methanol to precipitate the copolymer that wasformed. It was collected by filtration and dried overnight at 45° C. and1 mm Hg. The yield was 2.8 g (30%). Gel permeation chromatographyindicated that the product had a molecular weight (M_(n)) of 24,800 anda molecular weight distribution (M_(w)/M_(n)) of 1.7. NMR analysisindicated that the product was styrene-chloromethylstyrene copolymercontaining 20.4 mole percent chloromethylstyrene. The copolymer was usedin grafting experiments described below.

EXAMPLE 13

The styrene-chloromethylstyrene copolymers prepared above were graftedby using cobaloxime. Specifically, a sample of copolymer (1.02 g) wasmixed with methyl methacrylate (9.68 g), methyl ethyl ketone (1.81 g)and cobaloxime (0.05 g) and the mixture was heated for various times at70° C. The reaction mixture was filtered and the filtrate was added toexcess methanol to precipitate the product. Table VIII below gives thereaction times, the methyl methacrylate conversions, and the molecularweights of the various products from five different trials.

TABLE VIII Methyl Reaction Methacrylate Trial Time (Hr) Conversion (%)M_(n) M_(w)/M_(n) 1 1.1 9 29,700 17.6 2 2.6 15 28,200 52.7 3 7.5 23 — —4 19.4 32 27,100 72.0 5 70.4 36 — —

The product from Trial 3 was analyzed by NMR spectroscopy and it wasdetermined that the product contained 4.1 poly(methyl methacrylate)grafts per original copolymer molecule and an average of 6.5 methylmethacrylate units per graft.

EXAMPLE 14

The poly(chloromethylstyrene-co-styrene) prepared Example 12 was graftedwith methyl methacrylate as set forth in the previous example exceptthat zinc was used in addition to the cobaloxime. Specifically, thecopolymer (0.29 g), methyl methacrylate (0.93 g), methyl ethyl ketone(1.08 g), cobaloxime (0.018 g) and zinc powder (0.47 g) were admixed.The resultant grafted copolymer had a molecular weight (M_(n)) of 25,600and a molecular weight distribution (M_(w)/M_(n)) of 50. NMR spectrumindicated that the product contained 10 grafts per original copolymerchain and an average of 6.9 methyl methacrylate units per graft. Thisresult demonstrates that the presence of zinc increases the efficiencyof the grafting reaction.

EXAMPLE 15

In a similar fashion to the preceding examples,poly(isobutyl-methacrylate) was grafted topoly(chloromethylstyrene-co-styrene) by using cobaloxime. Specifically,copolymer (0.30 g), isobutyl methacrylate (0.88 g), methyl ethyl ketone(1.06 g), and cobaloxime (0.017 g) were admixed. The reaction mixturewas purged with argon and heated at 70° C. for two days. The product waspurified by Soxhlet extraction with methanol overnight. The product wasdetermined to have a molecular weight (M_(n)) of 18,300 and a molecularweight distribution (M_(w)/M_(n)) ratio of 7.9. NMR analysis indicatedthat the product had 4.6 poly(isobutyl methacrylate) grafts per originalcopolymer chain with an average of 4.8 monomer units per graft.

EXAMPLE16

In a similar fashion to the preceding examples, poly(ethyl acrylate) wasgrafted to poly(chloromethylstyrene-co-styrene) by using cobaloxime.Specifically, the styrene-chloromethylstyrene copolymer (1.02 g), ethylacrylate (10.1 g), methyl ethyl ketone (1.1 g), and cobaloxime (0.05 g)were admixed. The mixture was purged with argon and heated at 70° C. for7.8 hours. A second sample was heated for 70.8 hours. Products isolatedfrom these reactions were soluble in tetrahydrofuran, which indicatedthat they were not crosslinked. The sample that was heated for 7.8 hourswas determined to have an ethyl acrylate conversion of 11 percent, amolecular weight (M_(n)) of 34,100, and a molecular weight distribution(M_(w)/M_(n)) of 30.5. The sample that was heated for 70.8 hours wasdetermined to have an ethyl acrylate conversion of 34 percent, amolecular weight (M_(n)) of 33,400, and a molecular weight distribution(M_(w)/M_(n)) of 40.5.

NMR spectrum of the products indicated that the products contained anaverage of 3.1 grafts per original copolymer molecule.

What is claimed is:
 1. A polymerization process comprising the steps of:admixing a halogen-containing compound, monomer, a cobalt complex, andreducing agent.
 2. A polymerization process comprising the steps of:admixing a halogen-containing compound, monomer, and a cobalt complexselected from the group consisting of cobaloxime, organocobaloxime,cobalt porphyrin, and mixtures thereof, wherein the halogen-containingcompound is a polymer containing at least one carbon-halogen bond havingthe halogen atom bound pendant to the polymer backbone, bound to anorganic group that is pendent to the polymer backbone, or bound at thepolymer chain end, and the cobalt complex reacts with the at least onecarbon-halogen bond to form a radical capable of participating in acatalytic chain transfer or pseudo-living polymerization process.
 3. Aprocess for forming a methacrylate-functionalized polymer comprising thesteps of: admixing a halogen-containing polymer containing at least onecarbon-halogen bond having the halogen atom bound pendent to the polymerbackbone, bound to an organic group that is pendent to the polymerbackbone, or bound at the polymer chain end, a cobalt complex selectedfrom the group consisting of cobaloxime, organocobaloxime, cobaltporphyrin, and mixtures thereof, and a methacrylate ester, and heatingthe admixture, wherein the halogen-containing compound is a polymercontaining at least one carbon-halogen bond having the halogen atombound pendant to the polymer backbone, at the polymer chain end, orboth, and the cobalt complex reacts with the at least one carbon-halogenbond to form a radical capable of participating in a catalytic chaintransfer process with the methacrylate ester.
 4. A process for formingpolyacrylate-functionalized polymer comprising the steps of: admixing ahalogen-containing polymer containing at least one carbon-halogen bondhaving the halogen atom bound pendent to the polymer backbone, bound toan organic group pendant to the polymer backbone, or bound at thepolymer chain end, a cobalt complex selected from the group consistingof cobaloxime, organocobaloxime, cobalt porphyrin, and mixtures thereof,and acrylate monomer, and heating the admixture, wherein the cobaltcomplex reacts with the at least one carbon-halogen bond to form aradical capable of participating in a pseudo-living polymerizationprocess with the acrylate monomer.
 5. The process of claim 1, whereinsaid step of admixing is conducted in hexane, benzene, toluene, acetone,methylethyl ketone, tetrahydrofuran, methylcellusolve, dioxane, decalin,or mixtures thereof.
 6. The process of claim 1, wherein thehalogen-containing compound is a polymer containing at least onecarbon-halogen bond, where the halogen atom is bound pendant to thepolymer backbone, bound to an organic group that is pendant to thepolymer backbone, or bound at the polymer chain end.
 7. The process ofclaim 2, where the carbon in the at least one carbon-halogen bond isattached to a stabilizing group selected from phenyl groups, carbonylgroups, nitrile groups, vinyl groups, and substituted vinyl groups. 8.The process of claim 2, where said halogen-containing compound isselected from styrene-butadiene copolymers containingchloromethylstyrene units, brominated isobutylene-isoprene copolymers,and unsaturated polyesters containing reactive halogen atoms.
 9. Theprocess of claim 1, where said halogen-containing compound is selectedfrom CCl₄, CBr4, CBrCl₃, ΦCH₂Br, ΦCH₂Cl, CCl₃CH₃, ΦCHCl₂, CCl₃COCCl₃,and CCl₃ COOR, wherein R is an alkyl group, substituted alkyl group,aryl group, and substituted aryl group.
 10. The process of claim 1,where the monomer is a methacrylate monomer, vinyl aromatic monomer,methacrylamide, or mixture thereof.
 11. The process of claim 10, whereinthe methacrylate monomer is selected from methyl methacrylate, ethylmethacrylate, propyl methacrylate, t-butyl methacrylate, phenylmethacrylate, hydroxyethyl methacrylate, and N,N-dimethymethacrylamide.12. The process of claim 11, where the admixture contains from about 10to about 5000 parts by weight methacrylate monomer per one hundred partsby weight halogen-containing compound.
 13. The process of claim 1,further comprising the step of heating the admixture.
 14. The process ofclaim 13, where the admixture is heated to a temperature of about 70° C.15. The process of claim 2, where said admixture further comprises areducing agent.
 16. The process of claim 15, wherein said reducing agentis selected from zinc, iron, copper, and hydrogen.
 17. The process ofclaim 16, where said reducing agent is zinc.
 18. The process of claim 1,wherein said reducing agent is selected from zinc, iron, copper, andhydrogen.
 19. The process of claim 3, wherein the methacrylate monomeris:

wherein R includes an organic group.
 20. The process of claim 4, whereinthe acrylate monomer is:

wherein R³ includes an organic group.
 21. The process of claim 4, wheresaid step of admixing is conducted at a temperature from about 70° C. toabout 150° C.